FOUS30 KWBC 041626
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1214 PM EDT Tue May 04 2021

Day 1
Valid 16Z Tue May 04 2021 - 12Z Wed May 05 2021

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM EAST
CENTRAL MISSISSIPPI, ACROSS CENTRAL ALABAMA INTO NORTHWEST
GEORGIA...

1600 UTC update

The primary change to the previous Day 1 Excessive Rainfall
Outlook was to extend the moderate risk area farther to the
northeast across central Alabama into northwest Georgia.
Convection continues to enhance along and to the southeast of the
outflow boundary currently stretching across northern Alabama into
northern Mississippi. Concerns are for training of convection
over the next several hours along this outflow as the low level
flow become increasingly parallel to this boundary. This
convection may move over areas of northern Georgia into east
central Alabama that received heavy rains over the past 24 hours
and have lower ffg values. in areas of training hourly rainfall
totals of 1-3" possible. See WPC's mesoscale precipitation
discussion #0150 valid until approximately 2030 UTC for additional
information across this area.

A small slight risk area was also added across portions of south
central to southwestern Kentucky after collaboration with WFO LMK.
This area has received very heavy rainfall amounts over the past
24 hours. There is potential for additional scattered convection
this afternoon into this evening which may fall across areas that
have received the heavy precipitation, resulting in potential
runoff issues.

Elsewhere, the slight risk area was trimmed to the southeast
across western to central Tennessee by approximately 60 to 150
miles based on current radar trends.

Oravec


0900 UTC discussion

...Deep South into the Tennessee Valley...
The thermodynamic setup ahead of the approaching upper shortwave
trough remains favorable for heavy rain according to the latest
guidance, including low level moisture flux standardized anomalies
(3+ sigmas above the mean) and IVT values (at over above 1000
kg/(m*s)). Area of low pressure at the surface traversing the
northern TN and southern OH Valleys will likely result in multiple
heavy rainfall axes -- one farther north across much of TN into
southern KY associated with the frontal wave (deep-layer synoptic
support), where the instability will be sufficient (ML CAPE
1000-2000 J/kg) to support 1-1.5+ inch/hr rainfall rates. Lower
FFG values farther north also enhance the potential for flash
flooding, as depicted with the latest HREF exceedance
probabilities.

Farther south (Deep South/just inland of the central Gulf coast),
2000-4000 J/kg of ML CAPE partially induced by an eroding
mid-level capping inversion along with precipitable water values
~2" and convergent 850 hPa flow of 35-45 knots will allow for
hourly totals to 2.5" within the stronger, more organized
convection. Strong southwesterly mean flow should keep activity
fairly progressive until the front lays a bit more toward the
coast Tuesday night which will orient it more toward the mean flow
and could allow some repeating cells, which is shown most vividly
on the 00z FV3CAM. In terms of pinpointing an area of greatest
risk, while spread continues across MS and AL, the best guess as
to the area of higher impact currently is across southern MS and
southern AL in the middle of the expected instability pool, so per
coordination with the JAN/Jackson MS, BMX/Birmingham AL, and
MOB/Mobile AL, a Moderate Risk was added. More than a few pieces
of guidance (though usually high biased) indicate local amounts of 5-7"...believe local 3-6" amounts are most plausible considering
the frontal progression for much of the period. Higher potential
is theoretically possible closer to the Gulf Coast, depending upon
how mesoscale forcing/outflow boundary movement evolves Tuesday
night into Wednesday morning. If convective trends or the
guidance follows suit and trends southward later today, a
southward shift or expansion of the MDT risk is possible.


...Upper Ohio Valley...
The broad poleward flow of Gulf moisture brings 1.5 inch PWs
across the Midwest/Ohio Valley into PA and southeast NY which is 2
to 2.5 standard deviations above normal. Some instability,
occasionally over 1000 J/kg, will be enhanced by right entrance
jet forcing to allow localized heavy rain over what has been near
normal rainfall over the past two weeks. Therefore, a Marginal
Risk is maintained from KY through western PA into far western NY,
and expanded eastward to encompass heavy rain signals seen in the
guidance across northeast PA and in the vicinity of New York City.


Roth


Day 2
Valid 12Z Wed May 05 2021 - 12Z Thu May 06 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM SOUTHEAST
LOUISIANA TO SOUTHERN GEORGIA...

The cold front becomes more west to east oriented over the central
Gulf Coast Wednesday, allowing low-level inflow to be come nearly
parallel to the front and mean 850-500 mb flow. This brings an
enhanced potential for cell training within a favorable
thermodynamic environment (PWs 1.75-2.00 inches...mixed-layer
CAPES 1500-2500+ j/kg). With greater confidence of rainfall along
the central Gulf Coast from NOLA east along the FL/GA line, shrank
the Marginal Risk south a bit from central GA and removed from SC
which have been dry over the past week.

Jackson

Day 3
Valid 12Z Thu May 06 2021 - 12Z Fri May 07 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Jackson

$$
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FOUS30 KWBC 051543
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1142 AM EDT Wed May 05 2021

Day 1
Valid 12Z Wed May 05 2021 - 12Z Thu May 06 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG PORTIONS
OF THE CENTRAL GULF COAST...

1600 UTC update

Latest radar trends are showing the heaviest rainfall rates moving
offshore of eastern Louisiana, far southern Mississippi and far
southern Alabama. The slight risk was removed given these trends
and the marginal risk was suppressed southward by about 30-50
miles. The eastern end of the marginal risk area was trimmed back
to the west, taking it out of far southern Georgia and adjacent
north Florida as per 1200 UTC hi res guidance.

Oravec

0900 UTC discussion


...Central Gulf Coast...
A pre-frontal outflow boundary is laying near the coast currently
as the main upper low has ejected out, though a trailing
positively-tilted upper level shortwave is seen as significant
darkening on water vapor imagery across southeast TX and northwest
LA which may take some hours until it bypasses the region. There
have been attempts to shift the boundary offshore the MS and AL
coasts overnight, but the southerly movement in southeast LA
halted and recently reversed, raising concerns that the new
guidance may be correct in keeping/backing up the heavy rain
threat back to portions of southeast LA, southernmost MS,
southernmost AL and western FL panhandle coasts through the
morning into the early afternoon hours before the cold front
finally sweeps through the area. This is also when the guidance
shows a slight uptick in 850 hPa inflow, near or slightly
exceeding the mean 850-400 hPa wind in the area. ML CAPE of
1000-2500 J/kg remain to the south of the boundary (which should
continue to be the case), precipitable water values of 1.75-2"
remain along it, and effectively bulk shear should remain
sufficient for some organization. The concern would be increasing
saturation due to the ongoing and expected rainfall, so a Slight
Risk was hoisted in coordination with MOB/the Mobile AL forecast
office earlier and recently expanded west to New Orleans per more
recent coordination with LIX/the Slidell LA forecast office.

...Maryland/Virginia...
Showers and thunderstorms are expected to occur in two batches
today...one in the morning across northern MD and one in the late
morning/early afternoon from roughly DC south and eastward with a
frontal passage. Rainfall remains generally low over the past
couple weeks for the area, but the last couple days have seen two
distinct streaks of heavy rain near I-70 and I-66. Since the two
batches of rain/convection today do not appear to overlap, no
threat area is depicted, but if another concentrated corridor of
heavy rain intersects those of the past couple days or the urban
area, isolated issues can't be ruled out. The threat for
excessive rainfall is non-zero, but not quite up to to 5%
threshold.

Roth


Day 2
Valid 12Z Thu May 06 2021 - 12Z Fri May 07 2021

The remnant cold front stalls over the northern FL Peninsula
Thursday in deep layer westerly flow. Moisture advection off the
Gulf continues with PWs rising to around 1.75 inches which is two
standard deviations above the norm. With the surface front
parallel to the deep layer flow, instability present, and some
right entrance region upper level divergence from a jet streak
over GA there is potential for repeating cells with 1 to 2"/hr
rain rates on the northern Peninsula. This area has been dry
lately, so flash flood guidance is up around its normal 4"/hr in
this area. Therefore the excessive rain is low, but nonzero.
Uncertainty with placement of the front (the ECMWF remains farther
south than most other guidance) made for no Marginal Risk to be
drawn, but should frontal position confidence increase a need may
arise.

Jackson

Day 3
Valid 12Z Fri May 07 2021 - 12Z Sat May 08 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Jackson

$$
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FOUS30 KWBC 071530
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1130 AM EDT Fri May 07 2021

Day 1
Valid 16Z Fri May 07 2021 - 12Z Sat May 08 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Oravec


Day 2
Valid 12Z Sat May 08 2021 - 12Z Sun May 09 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL GREAT PLAINS AND ADJACENT MISSOURI VALLEY...

Heavy to potentially excessive rainfall is possible late Saturday
into early Sunday across parts of the Central Plains as a
deepening area of low pressures moves eastward. The 06/00Z NCEP
guidance has been consistently suggesting that rainfall rates will
be increasing during the evening in a region of low- to mid-level frontogenesis...especially once southerly winds tap enough
moisture to help increase instability (on the order of 1000 to
1500 J per kg)...and once the upper level flow becomes
increasingly difluent in response to a h25 mb low begins to take
of a neutral to modestly negative tilt over the Rockies. As a
result, storms should be increasingly capable of producing
downpours across parts of the Plains. While the anomalies
increase to between 1.5 and 2 standard deviations above
climatology...the actual precipitable water values remain in the
range of 1.25 to 1.5 inches and maximum equivalent potential
temperatures peak a little more than 330K. That should help limit
maximum rainfall rates...as will the fact that the NCEP guidance
and ECMWF have trended towards a more progressive solution
(although the GFS may be a bit too progressive). Finally, much of
the area has had below average rainfall over the past two weeks to
a month. As a result of collaboration/coordination with offices
in the area, the Slight Risk was downgraded to a Marginal Risk
area.

Bann


Day 3
Valid 12Z Sun May 09 2021 - 12Z Mon May 10 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
LOWER MISSISSIPPI REGION...

...Lower Mississippi Valley...

A cold front attached with the system moving into the Great Lakes
region on Day 2 should be pushing southward into the Lower
Mississippi Valley. That front will provide the focus for some
convection. Precipitable water values in excess of 1.5 inches will
be in place (which is in the 90th percentile for this time of
year) should be in place by the time the front arrives in parts of
Louisiana and Mississippi on Sunday afternoon. ARW-core ensemble
members are most aggressive in generating 2+ inches of rainfall in
24 hours while only two or three NMM members met that
threshold...with amounts apparently held in check by modest
instability. However, the area has experienced several rounds of
excessive rainfall in the previous few weeks which has made the
area more susceptible to excessive problems. Considering that the
best precipitable water values and mesoscale forcing only
partially overlaps the axis of greatest rainfall in the previous
30 days...felt no more than a Slight Risk was warranted at this
point. Later shifts will be evaluating and shifts in placement or
changes in the amount of rainfall forecast for further adjustments
to the outlook.

...Ohio Valley...
As the surface low pressure continues eastward from the Great
Lakes on Sunday, it will be spreading areas of moderate to locally
heavy rainfall into the Ohio Valley. Moisture influx will not be
as strong as it was farther west on Day 2 and the low level
isentropic left will also be weakening with time. As a result,
there amount of rainfall should not be as much as areas farther to
the west. While there was some heavy rainfall in parts of the
Ohio Valley during the past week or so, the areal coverage of the
heaviest rainfall was widely-scattered...meaning that much of the
area can still handle the amounts of rainfall expected without too
many problems. The main concern would be if there is enough
instability to result in sufficiently high rainfall rates or in
areas where terrain can be a factor.

Bann

$$
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FOUS30 KWBC 091606
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1205 PM EDT Wed Jun 09 2021

Day 1
Valid 16Z Wed Jun 09 2021 - 12Z Thu Jun 10 2021

...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
ARKANSAS AND MISSISSIPPI...

...ONGOING HEAVY RAIN OVER EXTREMELY SATURATED SOILS FROM
TUESDAY'S PROLIFIC RAINFALL CONTINUES FLASH FLOOD EVENT...

Northern Mississippi Delta...
A stalled mid/upper-level low will continue to focus heavy amounts
of precipitation for the Mid-South/ArkLaMiss. Under the base of
this system, the southwesterly flow will remain fairly
unidirectional through the low levels with max magnitude of 25kt
around 850mb with lighter flow above and below (which aids
redevelopment). Across northern LA, southern AR, and and northern
MS...PWs of 2" to 2.25" will continue to interact with MUCAPE of
1500-3500 J/kg which will continue to produce hourly rain totals
of 1.5 to 2". Unlike Tuesday, activity looks to be starting to
progress southeast a bit. Due to ongoing activity and threat for
overnight activity over similar areas, kept the High Risk as is,
shifted the Moderate Risk east a bit from AR/into northern AL.
Further updates are likely once the progression of the activity is
known and there is a better handle on location and magnitude of
the overnight activity.


Rest the the Eastern Third of the Lower 48...
Near and ahead of the weakening upper level trough, abundant
moisture will be in place throughout the region with precipitable
water values near or above 2" (2 standard deviations above
normal). Low-level inflow and the mean 850-400 hPa wind are weak,
which could lead to locally heavy downpours though convection
should struggle to organize. Instability should allow for
convection to mainly concentrate in the afternoon and evening
hours. The Slight Risk covers both the heavy rain potential and
portions of TN/KY/WV that either have had 200-400% of average
rainfall the past week and/or have lower flash flood guidance
values. May need to raise a Slight Risk for a portion of the
Mid-Atlantic coast where bay breeze interaction should help focus
activity.


...Northernmost MN...
Ongoing activity over northern ND will shift east with a surface
low along the central US/Canadian border. 12Z guidance continues
to agree that the best chance for any heavy rainfall will be
located to the east of the surface low in a region of upper level
difluence. The eastward shift in the Marginal Risk area reflects
similar shifts in the guidance that raise 700 hPa temperatures
above 12C across the Dakotas, which should act as a fairly
effective cap for convection -- MN is not as capped and the
surface low should be in the vicinity. Given rainfall from Monday
night into early Tuesday morning across the Northland/Arrowhead of
MN, some issues with runoff could occur in areas of repeat
convection. Expanded the Marginal Risk a bit south over northern
MN to include Duluth proper per the 12Z HRRR/NAMNest.

Roth/Jackson


Day 2
Valid 12Z Thu Jun 10 2021 - 12Z Fri Jun 11 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE TENNESSEE
VALLEY INTO PARTS OF THE MID-ATLANTIC REGION...

...Ohio Valley into the Mid-Atlantic Region...
The slow-moving system will continue to tap a moisture-laden
atmosphere to produce additional heavy...and potentially
excessive...rainfall along its track. Additional amounts of 1 to
3 inches are expected for areas already seeing ongoing flooding
and well above normal soil saturation of 200%+ in the Tennessee.
Depending on how slowly the heavy rainfall moves out of the
area...there may be enough overlap with areas recently soaked to
warrant an upgrade to Moderate...but too much uncertainty at this
point as to where that overlap may or may not occur. In the large
scale, though, PWAT anomalies continue to sit near 2.0-2.5 std
deviations above normal over this region. Given the changes made
to the Slight Risk area and Marginal Risk areas on Tuesday...only
change needed at this point was to account for somewhat better
agreement in terms of the western extent of QPF and to the risk
area along the Mid-Atlantic region as a cold front slowly makes is
way southward.

...Upper Midwest and Adjacent Western High Plains...
An upper low pushes out over the Western High Plains to the lee of
the Northern Rockies...setting up an broadly difluent upper level
pattern aloft and strengthening low level surface pattern that
keeps a flow of low level moisture over the region. Additional
pockets of 1 to 3 inches are expected...which can worsen any
ongoing flooding and lead to flooding in additional areas through
early Friday morning.

Bann


Day 3
Valid 12Z Fri Jun 11 2021 - 12Z Sat Jun 12 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID-ATLANTIC ON FRIDAY...

...Appalachians eastward to the Eastern Seaboard in the
Mid-Atlantic Region...
The threat of heavy to potentially excessive rainfall will
continue on Friday as the mid- and upper-level system makes it's
way from the Ohio Valley eastward...and then southeastward towards
southeast Virginia by early Saturday morning. With deep moisture
already in place, any convection that develops has the potential
to produce excessive rainfall via intense downpours. Some 1 to 2
inch per hour rates are possible given precipitable water values
of 2 inches (about 2.5 standard deviations greater than
climatology). Given broad weakness aloft, slow cell motion and
the potential for repeat convection will locally enhance the risk
of excessive rainfall.

...Upper Midwest...
Placed a Marginal Risk area over parts of North Dakota and
Minnesota mainly for convection early in the period associated
with a closed low that heads north of the International Border.
Precipitable water values are not expected to be terribly
anomalous, with the 1.25 to 1.5 inch values being little more than
1.5 standard deviations greater than climatology. That...combined
with the expectation that cells will be progressive...should limit
that risk of flash flooding. However, there still looks to be
some potential for convection early in the period to occur over
areas soaked in the preceding couple of days.

Bann

$$
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FOUS30 KWBC 101625
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1225 PM EDT Thu Jun 10 2021

Day 1
Valid 16Z Thu Jun 10 2021 - 12Z Fri Jun 11 2021

...THERE ARE MODERATE RISKS OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE MID-SOUTH AND MID-ATLANTIC...

...Lower MS Valley into the Southeast...
Backbuilding/training convection persists through midday over the
ArkLaMiss which is west of a stratiform shield associated with an
MCV that has drifted into north-central late this morning. Plenty
of upstream instability will help sustain convection as the focus
area continues to slowly shift south about 21Z. 16Z to 21Z an an
additional 2-4" of rain over the southwestern portion of the
current Moderate Risk which was essentially maintained from the
previous issuance. Numerous instances of flash flooding can be
expected into the afternoon hours...some of which may continue to
be significant in nature. Scattered activity overnight north of
the current area of precipitation, particularly from the 12Z 3km
NAM and recent HRRRs allows maintenance of the northern/eastern
part of the Moderate Risk as well as the Slight Risk.


...Ohio Valley through the Mid-Atlantic...
16Z Update...
Raised a targeted Moderate Risk over the immediate Washington DC
metro area, central to western MD into far southern PA for the
combination of ample heating raising instability, 1.8 to 2 inch
PWs which are 2 standard deviations above normal, and general
convergence from the slow moving cold front. Wind shear is the
lacking variable here as flow is so light through the column that
maintenance of heavy raining cells should be difficult. However,
the presence of bay breezes, the surface front, and terrain to the
west should allow for repeating cells to occur over the rather
urbanized area of Baltimore/Washington producing potentially
numerous instances of flash flooding.

A broad and slow moving mid/upper level trough and slow moving
back door cold front will result in scattered to widespread
convection this afternoon/evening from the Ohio Valley to the
central Mid-Atlantic coast. The environment will be conducive for
very heavy rainfall rates. PWs are above the 90th percentile, and
wet bulb zero heights around 13kft AGL are at the average maximum
for this time in June. Thus efficient warm rain processes will
likely dominate into tonight. Instability is likely a limiting
factor (where cloud cover has been thicker) for depth/intensity of cells...however the aforementioned moisture parameters would still
favor shallow low topped cells capable of very heavy rain rates.
The other limiting factor is longevity of cells at any one
location...as cells should generally pulse up and down rather
quickly. The weak instability potentially restricting the coverage
of heavier cells, and the short lived nature of most cells, may
prevent a more widespread flash flood risk today/tonight. However
slow cell motions and heavy short duration rates will likely still
be enough to result in scattered flash flooding through the Slight
Risk area.

There is certainly some potential for a more widespread and
significant event today over portions of WV and VA given the
efficient environment in place. A backdoor front dropping
southwestward will be a convective focus today, potentially
helping sustain a corridor of cell mergers...as it interacts with
terrain induced cells and slow moving cells downstream of the
front. The event today/tonight also has Moderate risk potential
over mountainous portions of WV/VA...but scattered flash flooding,
some locally significant, is the current expectation in this area.
We will continue to monitor trends this afternoon.

A bit better instability over the OH valley...but less of a focus
for cells. Thus cells should generally be smaller in scale and
thus any heavy rains will be quite localized. Expect isolated to
scattered flash flooding here this afternoon/evening...but on too
small of a scale to warrant anything more than a Slight Risk.


...Northern Plains...
Organized convection will push across the northern Plains this
evening into the overnight hours. Most indications are for a
progressive convective line generally near the slow moving frontal boundary...and thus would generally expect severe weather to be a
bigger risk than flash flooding. Cell merging at the onset of
initiation seems plausible over northeast MT and northwest ND and
12Z CAM guidance is strong enough to warrant an expansion of the
Slight Risk from central ND to the Canadian border. Portions of
north central SD and south central ND have however been very wet
of late...with a response noted in soil moisture and streamflow
anomalies. Thus if this area were to see 2"+ of additional rain
then some impactful flash flooding could occur, though 12Z
CAM/HREF guidance is less bullish for this area than overnight.
The 12Z HREF does highlight northern ND and eastern SD for FFG
exceedance and multi-year ARI potential. Therefore the Slight Risk
was expanded in ND where FFG is lower, but kept a Marginal in SD
where FFG is higher.


...Northern WI/MI...
Maintained a small Marginal risk across portions of northern
WI/MI. Convection this afternoon may result in locally heavy
rainfall across this region. Some of this area has seen locally
heavy rain of late, possibly making the region a bit more
susceptible...however long term conditions are still generally
dry. There may be some localized FFG exceedance. However, given
the overall antecedent conditions, and amounts likely just barely
exceeding FFG, impacts are likely to be minimal.

Chenard/Jackson


Day 2
Valid 12Z Fri Jun 11 2021 - 12Z Sat Jun 12 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID-ATLANTIC ON FRIDAY...

21Z Update...

...Appalachians eastward to the Eastern Seaboard in the
Mid-Atlantic Region...
The threat of heavy to potentially excessive rainfall lingers into
Friday as shortwave energy slowly makes its way eastward from the
Ohio Valley into the Mid-Atlantic region before being shunted
southeastward into southeast Virginia by Friday night/early
Saturday morning. The atmosphere will be plenty moist and
sufficiently unstable to support convection that produces some
intense downpours. Precipitable water values will be in excess of
1.75 inches along the track of the shortwave energy...with values
over 2 inches in place east of the Appalachians. Those
precipitable water values of or more inches are 2 to 2.5 standard
deviations above climatological average for mid-June.
Consequently, there is concern for flash flooding due to the
abundant moisture and slow cell motion. As mentioned previously,
eastern portion of VA and NC are among the most prone for flooding
considering that AHPS was showing soils at 300 to 600% of normal.

...Upper Midwest...
Maintained a low-confidence Marginal Risk area over parts of North
Dakota and Minnesota mainly for convection early in the period
associated with a closed low that heads north of the International
Border. Precipitable water values are not expected to be terribly
anomalous, with the 1.25 to 1.5 inch values being little more than
1.5 standard deviations greater than climatology. That...combined
with the expectation that cells will be progressive...should limit
that risk of flash flooding. However, there still looks to be
some potential for convection early in the period to occur over
areas soaked in the preceding couple of days.

Bann


Day 3
Valid 12Z Sat Jun 12 2021 - 12Z Sun Jun 13 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PARTS OF
THE SOUTHEAST U.S. AND WEST TEXAS...

...Southeast U.S....
Maintained a Marginal Risk area over portions of the southeast
U.S. given some lingering rainfall before the slow-moving system
finally moves off-shore. The consensus of the global model
guidance is that any additional moderate to heavy rainfall in the
Day 3 period should be from central North Carolina or
southward...which would be south of the area that has had areas of
5 inches of rain in the previous week plus any additional rainfall
that falls on Day 2. Even so, the area of North Carolina into
South Carolina and Georgia have had some pockets of 2 to 5 inch
amounts, so any downpours could result in localized flooding
concerns. Given the poor track record of how the models have
handled the timing of this system over the past days, opted to
depict a broader Marginal Risk than might be expected for the
deterministic QPF simply based on uncertainty.

...Texas Panhandle and Adjacent Portions of New Mexico...
High pressure located over the central and southern Plains will
begin to weaken and shift eastward during the day, allowing low
level winds to become southeast across the Texas panhandle and
adjacent portions of New Mexico by late afternoon or early
evening. The increased moisture availability should allow for
enough destabilization to allow scattered showers and
thunderstorms capable of producing locally heavy rainfall to form.
The outlook area is farther north than some places in West Texas
that have received 1 to locally 2 inch rainfall amounts in the
past week. At the moment, the GEFS had more ensemble members
showing 1+ inch contour over the area than the SREF during the 24
hour period. However, given the arrival of increased moisture due
to the southeasterly flow in low levels, felt a Marginal was
warranted.

Bann

$$
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FOUS30 KWBC 151542
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1141 AM EDT Thu Oct 15 2020

Day 1
Valid 12Z Thu Oct 15 2020 - 12Z Fri Oct 16 2020

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

An increase in moisture (PWs climbing above 2") and sufficient
instability (2000+ J/kg) across southern Florida this
afternoon/evening will result in the development of thunderstorms
capable of producing very localized heavy rainfall. The 12Z hi-res
guidance shows some low-end probabilities for exceeding 1-2" in
1-hr, though the majority of the guidance keeps the better
instability and axis of heaviest rainfall offshore. With
relatively weak mean flow (under 10 kts), storms may be slow
moving and if develop over particularly sensitive locations
(urban, poor drainage areas) some localized flooding will be
possible. But given the lower confidence in storm coverage and
intense rain rates, a Marginal Risk was not introduced with this
update.

Taylor


Day 2
Valid 12Z Fri Oct 16 2020 - 12Z Sat Oct 17 2020

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

...New England...
Guidance continues to show wave development along an East Coast
front during Fri/Fri night with the surface low reaching close to
the New England coast by the end of the period early Sat. Expect
rainfall rates to be well below short-term FFG values at least
from Fri into early Fri night. Later Fri night/very early Sat the
best consensus shows a band of enhanced moisture (precipitable
water values reaching approximately 1-2 standard deviations above
normal) streaming northward, most likely into southeastern and
central New England. Given that instability parameters do not
appear favorable for embedded convection, the 00Z Nam Nest
3/6-hour rainfall rates over western Maine in the 06Z-12Z Sat time
frame seem to be overdone. Otherwise the composite of highest
rainfall rates and 1/3/6-hour FFG does not lend itself yet to
depicting a Marginal Risk area. In most guidance the best
rainfall rates do not quite reach central/northern Maine where FFG
values are lower, while southeastern New England may see a period
of higher rainfall rates but has higher FFG values. The primary
issue will likely be water collecting in areas with poor drainage.

Rausch


Day 3
Valid 12Z Sat Oct 17 2020 - 12Z Sun Oct 18 2020

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

...Maine...
Models agree that a sharpening shortwave aloft progressing
northeastward across New England will strengthen low pressure that
should track from near the New England coast north-northeast into
Canada. As this development occurs, an axis of precipitable water
values of around 1-2 standard deviations above normal will likely
cross the state of Maine. Some guidance shows potential for
localized 1-1.5 inch per six hour rainfall rates which could get
close to FFG values over central and northern Maine where recent
rainfall has been well above normal. Guidance spread in specifics
is still great enough to keep confidence low in defining a
specific area that would warrant a Marginal Risk at this time. As
in the Day 2 period, the most likely threat will be for water
collecting in areas with poor drainage.

Rausch

Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt

$$
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FOUS30 KWBC 021955
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
354 PM EDT Fri Oct 02 2020

Day 1
Valid 16Z Fri Oct 02 2020 - 12Z Sat Oct 03 2020

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
FAR SOUTHERN FLORIDA...

...Southern Florida...
16Z Update: No significant changes were made to the outlook at
this time. A combination of deep, tropical moisture (PW over 2
inches), moderate instability with a tall, narrow CAPE profile,
and deep layer mean wind around 5 knots should support rain rates
in excess of 2 inches per hour if strong convection redevelops.
One potential issue could be a canopy of mid-high level cloud
cover from a cluster of convection about 70mi NW of Key West (at
1530Z) over the Gulf of Mexico. That could restrict instability
more than models are projecting and limit convective intensity
today. Nevertheless, the overall environment is sufficiently
supportive of very heavy rain rates that the Slight Risk area is
maintained.

Previous Discussion: A deep upper level longwave trough positioned
across the eastern two-thirds of the CONUS will remain anchored
through the forecast period as a series of shortwaves help to
sharpen a jet across the Southeast coast. As a result, upper
level divergence will strengthen atop of a quasi-stationary
surface front draped over southern Florida. The tropical airmass,
along and south of this boundary, is clearly depicted by
precipitable water values ranging between 2-2.25 inches and
MUCAPE values around 500-1000 J/kg. With sufficient large scale
lift, confluent low level flow, moisture and instability in place,
anticipate efficient rain rates, similar to what has been observed
over the past 24 hours. With steering flow out of the southwest
and boundary layer easterly winds, anticipate storms to be slow
moving, potentially backbuilding, along/south of the
aforementioned boundary. This will inevitably exacerbate hourly
rainfall totals.

According to the latest 00Z high resolution model guidance, hourly
rain rates may reach 2-3 inches per hour which is supported by the
above thermodynamics and the latest HREF neighborhood
probabilities. And based on the position of the surface front,
expect the highest rainfall totals through early Saturday to occur
across portions of far southern and southeastern FL. Areal
average precipitation will range between 1-3 inches with locally
higher amounts anticipated. Given the wet antecedent conditions
and the latest uptick in WPC QPF across portions of southern FL,
the Slight Risk was extended south and west with the Marginal Risk
expanded as well. Therefore, anticipate localized to scattered
flash flooding, especially across locations that have already
observed quite a bit of rain through the past 24 hours (along
portions of the east-central FL coast) and over urban corridors.

Pagano


Day 2
Valid 12Z Sat Oct 03 2020 - 12Z Sun Oct 04 2020

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE
ATLANTIC COAST OF FLORIDA...


...Florida...

20 UTC update...

Only minor adjustments were needed for this update to the day 2
excessive rainfall outlook based on the latest guidance. Previous
setup and thoughts as described below still stand. A slight risk
remains along the Florida Atlantic Coast from roughly Miami to
north of Daytona Beach, with a marginal risk covering the
remainder of the southern two thirds of the Peninsula.

Santorelli

Previous discussion issued at 0754 UTC...

A favorable setup for periods of heavy rainfall will continue
Saturday as a stationary boundary lingers across the Florida
Peninsula. During Saturday, this front will likely begin to lift
northward as a warm front, spreading better instability and
moisture northward as far as the First Coast. This front will
retreat to the northwest both in response to increased low-level
ridging off the Southeast Coast, and the approach of an amplifying
longwave trough which should dig into the TN Valley by Sunday
morning. The NW displacement of this front will drive instability
as high as 1500 J/kg MUCape across much of the southern half of
the Peninsula and along most of the Atlantic Coast, with PWs also
surging above 2.25", approaching +3 standard deviations above the
climo mean, and near or above daily records according to the SPC
sounding climatology. These favorable thermodynamics will be acted
upon by a strengthening upper jet streak leaving the favorable
diffluent RRQ and an upper divergence maxima across the state,
with 850mb S/SE inflow increasing to 20-30 kts to drive deep layer
ascent progged by omega maxima spreading northward. A lack of bulk
shear indicates that storms may be of the pulse variety Saturday,
however, training along the front and parallel to the upper jet
streak suggests training will be of concern, with some
backbuilding possible along the Atlantic Coast as the front lifts
northward. Parts of the east coast of FL have received excessive
rainfall in the past 24 hours, with additional heavy rain likely
on Friday. Depending on where the heavy rain occurs on D1, an
expansion of the SLGT risk may be needed, but at this time the
greatest threat for flash flooding appears to be confined to the
east coast where antecedent rainfall has been greatest and
ensemble probabilities for 3" are the highest. The MRGL risk
covers much of the rest of the peninsula where periods of heavy
rainfall are possible.

Weiss



Day 3
Valid 12Z Sun Oct 04 2020 - 12Z Mon Oct 05 2020

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHERN AND CENTRAL FLORIDA...

20 UTC update...

Only notable change to the previous day 3 excessive rainfall
outlook was to expand the slight risk a bit to the southwest to
include the Tampa Bay region. This is due to slight model
increases in QPF for that region, likely associated with moisture
ahead of newly upgraded T.D. Twenty-Five located near the Yucatan
Peninsula. See previous discussion for more details regarding both
Florida and the marginal risk along coastal North Carolina.

Santorelli


Previous Discussion issued at 0755 UTC...

...Florida...
A continuation of heavy rainfall from Saturday is likely on
Sunday, but with a northern displacement and potential enhancement
across parts of Northern Florida.

Nearly stalled warm front will linger across the central or
northern part of the Florida Peninsula Sunday. This boundary will
serve as a focus for thunderstorms, with a sharp moisture and
instability gradient developing along it. At the same time, a
sharpening longwave trough will be pushing eastward into the
Southern Appalachians, with a downstream jet streak becoming more
significantly poleward oriented and strengthening to a core of
150+ kts across ME, above the 97th percentile for wind speed for
early October. This leaves a robust diffluent RRQ atop Florida,
with a divergence maxima lingering in place across the Southeast.
The lift associated with this RRQ will likely drive stronger
frontogenesis along the baroclinic zone, enhancing low-level
convergence to drive robust deep layer ascent. Additionally, the
overlap of upper ventilation and low-level convergence may lead to
surface low development to further enhance rainfall potential.
While all of this is occurring, a tropical disturbance near the
Yucatan Peninsula of Mexico will spread high PWs in excess of
2.25" northward, and there is potential for a Predecessor Rain
Event (PRE) from late D2 into D3 across parts of N FL along the
western edge of a 925mb theta-e ridge >340K.

Favorable thermodynamics noted by MUCape approaching 1500 J/kg and
anomalously high PWs in an environment with warm cloud depths
exceeding 16,000 ft will drive rain rates which at times will
likely exceed 2"/hr. Generally slow storm motions to the northeast
should train, which with these rain rates could cause flash
flooding across parts of the region. While there remains some
spread into the amplitude and placement of the heaviest rainfall,
mostly due to differences in the frontal placement and amplitude
of the longwave trough, the SLGT risk was drawn to match the
highest ensemble probabilities for 3" of rainfall, with higher
amounts certainly possible, if not likely. While FFG across the
SLGT risk area is generally 3-4"/3hrs, some of this will likely be
compromised by heavy rainfall on D2, and exceedance of these
thresholds is becoming more likely. A MRGL risk surrounds the SLGT
risk area from far SE GA into central FL where heavy rain is also
possible, but the signal for flash flooding is less robust.


...Coast of North Carolina...
Guidance has trended upward with rain along the immediate coast of
NC from Cape Fear into the Outer Banks. A plume of tropical
moisture with PWs above 2" is likely to stream northeast from a
tropical disturbance near the Yucatan Peninsula. This moisture
lifting northeast will interact with a complex surface pattern,
including a stationary front/coastal front, and a powerful upper
jet streak placing favorable diffluence for ascent along the
coast. The heaviest rainfall may remain just offshore depending on
the speed and amplitude of an approaching longwave trough from the
west, but guidance has trended slightly more amplified and slower,
pulling heavy rainfall back onto the coast on Sunday. Despite
generally high FFG of 2.5-3.5"/3hrs, training of rainfall rates
greater than 1"/hr are possible which could lead to flash
flooding.


Weiss



Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt


$$
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FOUS30 KWBC 030816
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sat Oct 03 2020

Day 1
Valid 12Z Sat Oct 03 2020 - 12Z Sun Oct 04 2020

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG THE EAST
COAST OF FLORIDA...

Periods of heavy rainfall will continue across the FL Peninsula
associated with a stationary surface boundary. As this front lifts
north as a warm front, better instability and moisture will also
spread north through the afternoon. By late Saturday this front
will begin to retreat to the northwest in response to increased
low-level ridging off the Southeast Coast, and the approach of an
amplifying longwave trough which will dig into the TN Valley. The
displacement of this front will drive instability as high as 3000
J/kg MUCape across portions of the southern half of the Peninsula.
Precipitable water values will also surge above 2.25", approaching
+3 standard deviations above the climo mean, and near or above
daily records according to the SPC sounding climatology. These
favorable thermodynamics will be aided by a strengthening upper
jet streak leaving the favorable diffluent right entrance region
across the state. With boundary layer southerly/southeasterly
20-30 knot flow and deep layer steering flow out of the southwest,
convection should be fairly progressive south of the front, though
training may occur. Closer to the surface boundary, anti-parallel
corfidi vectors may help produce more slow moving/backbuilding
storms.

Given the potential for training, slow/back building storms and
the resurgence of better instability and confluent flow,
especially as the front lifts north, anticipate the heaviest rain
to focus along the east coast. Areal average precipitation through
the forecast period will range between 1-3+ inches along and just
inland of the coastline with hourly rain rates exceeding 2 inches
per hour at times which is supported by the latest HREF
neighborhood probabilities. Given parts of this region has
received over 400% of normal precipitation over the past several
days, felt any additional heavy rain could lead to flash flooding
concerns, especially across the urban corridors. Therefore, the
Slight Risk area was modified to account for this potential which
was based on the latest WPC QPF. Across the rest of the peninsula,
expect scattered convection to produce between 0.25-1+ inches of
rain with localized flash flooding possible.

Pagano


Day 2
Valid 12Z Sun Oct 04 2020 - 12Z Mon Oct 05 2020

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHERN AND CENTRAL FLORIDA...

...Florida...
Heavy rainfall from Day 1 /Saturday/ is likely to continue into
Day 2 /Sunday/ as a warm front stalls across the Florida Peninsula
before drifting back to the south as a cold front late Sunday.

This warm front will lift slowly northward early Sunday before
stalling and pushing back south as a cold front in response to a
wave of low pressure developing off the Southeast coast. This
surface low will develop due to an intensifying jet streak
pivoting northward into New England, leaving strong upper
ventilation within the robust diffluent RRQ overhead. This jet
streak combined with the low-level baroclinic zone will drive
surface low development, and as this low lifts northeast the
latter half of D2, the boundary will likely sink back to the
south. While guidance has backed off somewhat on QPF, there is
still a strong potential for training heavy rainfall which may
lead to flash flooding, so the SLGT risk continues with only minor
adjustments.

PWs across the Florida Peninsula will remain anomalously high,
2.25+", as moisture associated with tropical storm Gamma gets
drawn northeastward from the Yucatan Peninsula. This high PW will
combine with MUCape reaching 1500 J/kg and warm cloud depths
nearing 16,000 ft to provide favorable thermodynamics for heavy
rainfall. Rain rates are likely to reach 2"/hr at times, and
despite 0-6km mean winds of 10-15kts suggesting fast individual
cell motions, training along the boundary is likely as evidenced
by parallel propagation vectors. This indicates that some areas
may receive several rounds of heavy rainfall Sunday, and this
could occur on top of areas that have received in excess of 300%
of normal rainfall the past 14 days. As the front sags southward
again late in the period, the low-level convergence along it will
become increasingly disconnected from the upper diffluence to
slowly cause waning of the deep layer ascent. However, the
anomalous thermodynamics will persist, so any convection could
still produce heavy rainfall. After coordination with WFO JAX and
MLB, the SLGT and surrounding MRGL risk were pulled southward just
slightly to better encompass areas that have received excessive
rainfall and flooding this week.

...Coast of North Carolina...
The MRGL risk was trimmed away from SE North Carolina and now only
includes extreme coastal eastern NC from Cape Lookout to near Nags
Head. This change is due to an eastward shift in QPF among the
guidance, likely due to a more progressive mid-level trough
leading to further east placement of the diffluent RRQ of the
downstream upper jet streak, as well as the surface low. Despite
the lowered QPF, maintained the MRGL for extreme eastern NC where
at least modest instability may lift onshore ahead of the surface
low, allowing for rain rates to exceed 1"/hr. This is where the
ECENS and GEFS ensembles still indicate a low-chance for 3+" of
rainfall which could locally exceed the FFG.

Weiss


Day 3
Valid 12Z Mon Oct 05 2020 - 12Z Tue Oct 06 2020

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Weiss

Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt

$$
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FOUS30 KWBC 080733
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
233 AM EST Sat Feb 8 2025

Day 1
Valid 12Z Sat Feb 08 2025 - 12Z Sun Feb 09 2025

...West Virginia...

Strong N-S quasi-zonal mid and upper level flow will be perturbed
a bit during Day 1 (12Z Sat-12Z Sun) as a 150+ kt upper level jet
streak traverses the Upper Midwest and Ohio Valley, while a flat
500 mb vort lobe pushes across the Lower Great Lakes. Broad-scale
exit region forcing associated with the upper jet axis will surge
southwesterly low-level inflow ahead of the surface frontal wave,
with 850 mb moisture flux anomalies peaking between 4-5 standard
deviations above normal later this afternoon into Sat night, while
TPW values peak around 1". Robust synoptic-scale support and low-
level moisture transport will be offset somewhat by the weak
elevated instability, with MUCAPEs generally less than 500 J/Kg.
Nevertheless, even though not advertised on the latest (00Z Sat)
HREF, the aforementioned dynamic and thermodynamic ingredients will
be sufficient for spotty hourly rain rates of 0.5"+ and 3-hourly
rates of 1.0"+, with localized event totals between 1.5-2.0"+.

Current 3-hr flash flood guidance values remain quite low (1" or
less) across the outlook area, which includes much of WV. Despite
the lack of instability, the low FFG values could be exceeded over
isolated areas with 2 consecutive hours of 0.5"+/hr rainfall rates.
Since the soils in these areas are saturated, and the terrain is
rugged, we have maintained the Marginal Risk area for much of WV
(outside of its northern or eastern Panhandles).

Hurley/Roth


Day 2 Valid 12Z Sun Feb 09 2025 - 12Z Mon Feb 10 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 3
Valid 12Z Mon Feb 10 2025 - 12Z Tue Feb 11 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley

$$
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FOUS30 KWBC 090808
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
308 AM EST Sun Feb 9 2025

Day 1
Valid 12Z Sun Feb 09 2025 - 12Z Mon Feb 10 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 2
Valid 12Z Mon Feb 10 2025 - 12Z Tue Feb 11 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 3
Valid 12Z Tue Feb 11 2025 - 12Z Wed Feb 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE MID-SOUTH AND LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY...

...ArkLaTex-ArkLaMis into the Mid-South and Tennessee Valley...
Strong NW-SE upper level jet streak will dive southeast into CA
late on Day 3 (Tue night) -- on the western periphery of the
longwave trough towards the base. As this occurs, the broad western
U.S. trough will amplify, thereby enhancing the deep-layer ascent
and southwesterly flow/moisture transport within a maturing Warm
Conveyor Belt (WCB) downstream across the Mid South-Lower MS Valley
and TN Valley. 850-700 mb moisture flux anomalies increase to 2-3
standard deviations above normal Tue-Tue night, while TPW values
climb to 1.5-1.75" (around +2 standard deviation above normal). The strengthening dynamical and thermodynamical support will make for
efficient rainfall rates despite the lack of deep-layer
instability. Much of the guidance, non-CAM at this point being a
Day 3 forecast, depicts a widespread swath of 1.5-2.5" of rain
within the outlook areas, with more stripes of >3" within the
Slight Risk area. Storm motions nearly parallel to the WSW-ENE
oriented surface boundary will boost the potential for training,
and even though currently the non-CAM guidance is advertising
meager deep-layer elevated instability (MUCAPEs generally 250-500
J/Kg), believe these values will be amplified somewhat as the event
gets within the high-res CAM windows, again given the dynamic and
thermodynamic response to the broad-scale upper trough amplification.

2.00"+/3hr rainfall rates are anticipated where the cells do
train, again most likely within the Slight Risk area, which could
lead to localized-scattered instances of flash flooding.

Hurley

$$
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FOUS30 KWBC 100829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
329 AM EST Mon Feb 10 2025

Day 1
Valid 12Z Mon Feb 10 2025 - 12Z Tue Feb 11 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Beginning Monday afternoon, an increase of convergence on the nose
of 850mb flow extending from Texas into Tennessee will support an
increase in light to moderate rain and a few rumbles of thunder
from eastern Oklahoma through Kentucky/Tennessee. Rain rates are
expected to be modest (around 0.25-0.5 inch/3-hour period),
although some of this rainfall will eventually reach areas of
southeastern Kentucky where soils are moist and sensitive from
antecedent rainfall. The relatively short duration of light to
moderate rainfall in this area precludes an introduction of
Marginal/5% risk probabilities, although one may be needed in later
outlook updates if a longer duration of rainfall (greater than 3-6
hours) becomes apparent across southeastern Kentucky.

Cook


Day 2
Valid 12Z Tue Feb 11 2025 - 12Z Wed Feb 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE MID-SOUTH AND LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY...

...ArkLaTex-ArkLaMis into the Mid-South and Tennessee Valley...
Increasing coverage of showers and thunderstorms along and ahead of
a well defined cold front trailing a developing area of low
pressure taking shape over the Tennessee Valley will lead to an
increasing threat of excessive rainfall Wednesday into early
Thursday from easter Texas and parts of Arkansas and Louisiana
into the west aspect of the Appalachians of Tennessee and southeast
Kentucky. At the synoptic scale, a broad trough over the western
U.S. will amplify, thereby enhancing the deep-layer ascent and
southwesterly flow/moisture transport over this part of the country
due to a increasing low level flow. 850-700 mb moisture flux
anomalies still look to increase to 2-3 standard deviations above
normal Tuesday/Tuesday night while Precipitable Water values climb
to 1.5-1.75" (around +2 standard deviation above normal). The
strengthening dynamical and thermodynamical support will make for
efficient rainfall rates despite the lack of deep- layer
instability and the exit region of a 125 to 150 kt upper level jet
should aid deep layer vertical ascent. Much of the guidance
generally depicts a widespread swath of 1.5-3" of rain within the
outlook areas, with the most aggressive model being the ECMWF with
maximum values exceeding 4 inches. Storm motions nearly parallel
to the WSW-ENE oriented surface boundary will boost the potential
for training despite meager deep- layer elevated instability
(MUCAPEs generally 250-500 J/Kg). With 2.00"+/3hr rainfall rates
still being anticipated where the cells do train, again most
likely within the Slight Risk area, which could lead to localized-
scattered instances of flash flooding.

Bann


Day 3
Valid 12Z Wed Feb 12 2025 - 12Z Thu Feb 13 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
TENNESSEE VALLEY INTO THE MID-SOUTH,,,

...Tennessee Valley into the Mid-South...
The threat of excessive rainfall will continue on Wednesday and
early Thursday ahead of the same system which brought the
excessive rainfall potential on Tuesday into early Wednesday as a
cold front makes its way eastward. Broad scale ascent will continue
to aided by the southern entrance region of a 135 to 155 kt upper
level jet...while moisture convergence is maximized along a well
defined surface cold front which intercepts a plume of moisture
being pulled northward by a 40 to 50 knot low level jet. There is
still spread in the guidance about placement of where the heaviest
rainfall will occur but amounts generally in the 1 to 3 inch
range...with locally higher amount where any enhanced rainfall
rates set up due to banding/training. Given antecedent
conditions...feel that a Slight risk should suffice.

...California Coast...
The plume of moisture from the Pacific Ocean towards the end of Day
2 will start to bring rain to the coastal areas during the Day 3 period...beginning in northern and central portions of California
on Wednesday that propagates southward during Wednesday night and
Thursday. Present indications are that the heaviest amounts remain
off shore...but a general uptick in amounts was noted over the past
24 hours in this area.

Bann

$$
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FOUS30 KWBC 110836
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
336 AM EST Tue Feb 11 2025

Day 1
Valid 12Z Tue Feb 11 2025 - 12Z Wed Feb 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE MID-SOUTH AND LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY...

Few changes needed to the old Day 2 ERO as it propagates into the
Day1 period. Main focus for heavy rainfall and the potential for
excessive rainfall will be along and ahead of a cold front
associated with a developing synoptic scale low pressure system
within a broad/fairly flat flow pattern. Inclusion of more CAM
guidance supports the idea of higher intensity rainfall extending
as far west as eastern Texas...a tendency we often see convection
get organized farther southwest than expected in events like this,
and there is growing QPF signal in the 12z ECMWF, UKMET and Gem Reg
over this area. The Slight risk area extended northeastward where
there is a bit of instability that develops later in the period but
looks to be lacking initially. At expect the flash flood risk to
pick up more over this area as we head into day 2.

Bann


Day 2
Valid 12Z Wed Feb 12 2025 - 12Z Thu Feb 13 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
TENNESSEE VALLEY INTO THE MID-SOUTH...

...Tennessee Valley into the Mid-South...

The prolonged heavy rainfall event will continue om Wednesday into
Wednesday night over the Southeast. The extended duration of this
event will lead to storm total rainfall into the 3-5" range, with
locally higher totals possible. As stronger forcing ejects eastward
on Wednesday, an increase in the low level jet should aid in both
increasing moisture convergence and advecting instability
northward. The best overlap of ingredients that has the potential
for excessive rainfall looks to be over parts of AL/GA into far
southwest Tennessee. This is approximately the same area as the
previous Day 3 outlook...and given no major shifts in the synoptic
pattern saw little reason to make too many changes.

...California Coast...
The plume of moisture from the Pacific Ocean towards the end of Day
2 will start to bring rain to the coastal areas during the Day 3 period...beginning in northern and central portions of California
on Wednesday that propagates southward on Wednesday night and
early Thursday. Present indications are that the axis of the
Atmospheric River and the associated heaviest amounts remain off
shore or right along the coastal terrain...but a general uptick in
amounts was noted over the past 24 hours in this area.

Bann


Day 3
Valid 12Z Thu Feb 13 2025 - 12Z Fri Feb 14 2025

..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL PARTS OF THE
SOUTHERN CALIFORNIA COAST...

There is a Moderate Risk of excessive rainfall over portions of the
Southern California coast embedded within a broader Slight risk of
excessive rainfall covering much of the central and southern
California coast. An atmospheric river is expected to skirt the
coast as it makes its way south and east. The primary concern is
for damaging flooding and debris flow from the numerous fresh burn
scars in the region given the 24-hour QPF in the 1.5 to 3.5 inch
range...with potentially localized higher amounts. In
addition...the area is highly urbanized and an environment in which
much of the rainfall will turn immediately to runoff. Farther
north...the Slight risk was extended into portions of the
Sacramento Valley and San Joaquin Valley...where QPF is not
expected to be as great but the conditions have been wetter and
soils are more saturated than soils farther south.

Bann

$$
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FOUS30 KWBC 120741
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
241 AM EST Wed Feb 12 2025

Day 1
Valid 12Z Wed Feb 12 2025 - 12Z Thu Feb 13 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF THE
DEEP SOUTH AND COASTAL AREAS OF CALIFORNIA...

Large Marginal and Slight Risk areas extend from Louisiana to the
central Appalachians and portions of Virginia. The Marginal and
Slight Risk areas cover multiple regimes for excessive rainfall potential:

1) Long-duration, moderate to heavy rainfall along an axis
extending from east Texas (beginning at 12Z) east-northeastward
into northern Georgia and the southern Appalachians. Much of this
axis has experienced appreciable antecedent rainfall amounts (in
the 2-3 inch range on February 11) and models are consistent in
depicting at least one more round of heavy rain across that same
axis as a thunderstorm complex organizes and moves east-
northeastward from in Texas later this morning. Another 1-3 inches
of is expected (heaviest from western in to central Mississippi).
Given the wet soils from prior rainfall, several instances of
flash flooding are expected from central Louisiana through the
southern Appalachians and northern Georgia.

2) Somewhat lighter rainfall should occur across portions of
Virginia and West Virginia through the day. Not only are soils
water-logged and streamflows above average across these areas, but
recent snow/ice could melt under persistent warm advection and
temperatures slowly rising above freezing through the forecast
period. Light to moderate rainfall could enhance excessive
runoff/ponding especially in sensitive areas and low spots.

3) CAMs are in very loose agreement in depiction of east-west
oriented outflow boundary left behind by convective complex(es)
across portions of southern MS/AL through early afternoon. Strong south-southwesterly 850mb flow and abundant moisture should result
in reignition of deep convection focused along boundaries for much
of the afternoon and early evening. The orientation of these
boundaries should focus convective development and may allow for
training and intense rainfall rates at times. This is supported in
particular by the 00Z HRRR, which depicts 5-9 inch rain amounts
across southern Alabama through 12Z Thursday. Uncertainty in the
specific placement of boundaries/heavy rainfall corridors and dry
antecedent conditions are factors that preclude a higher risk,
although some higher-end flash flood potential exists in this
scenario - especially if complexes can materialize over more
populated areas of LA/MS/AL/GA.

Cook


Day 2
Valid 12Z Thu Feb 13 2025 - 12Z Fri Feb 14 2025

..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL PARTS OF THE
SOUTHERN CALIFORNIA COAST...

...California...
The peak of the atmospheric river is expected during this period
with the initial focus on coastal central California at the start
of the period, then the best IVT shifts southward through the
period, reaching southern California by the end of the period
Thursday night. IVT values from the GFS peak at around 600-700
kg/m/s initially along the central coast then settle around 400-500
kg/m/s as the AR reaches SoCal. The greatest QPF amounts will be
confined to the coastal terrain areas as well as for the Sierra.
Total amounts for the 24-hour period look to be between 1-3" with
the favored terrain areas and peaks topping out between 4- 6"+.

The primary concern is the potential for damaging and potentially life-threatening burn scar flash flooding and debris flows,
particularly for southern California where the Moderate Risk (Level
3/4) is in place. Even outside the burn scar regions, the intense
rain rates and rainfall totals over the highly urbanized area could
bring scattered to numerous instances of flash flooding. Elsewhere,
a broad Slight Risk (Level 2/4) exists for much of the coastal
ranges as well as the Central Valley and lower elevations of the Sierra Nevada.

A Moderate Risk of excessive rainfall continues from yesterday's Day
3 ERO across portions of the Southern California coast, and for the
new Day 2 ERO was expanded slightly on the northwest side to
encompass the Lake Burn Scar (2024), while also eastward to include
the southwest San Bernardino Mountains, including the Line Burn Scar
(also 2024). Again, the primary concern is for damaging flooding and
debris flow from the numerous fresh burn scars in the region given
the 24-hour QPF in the 1.5 to 3.5 inch range (with localized higher
amounts). In addition, the area is highly urbanized and an
environment in which much of the rainfall will turn immediately to runoff.

Farther inland, given the QPF trends and snow levels, the Slight
Risk was extended into eastern portions of the San Joaquin Valley
and southern Sierra/adjacent foothills. This expansion includes the
Borel burn scar (2024).

...Florida Panhandle and Southern Georgia...
Lingering heavy rainfall will continue Thursday across portions of
the Florida Panhandle and southern Georgia, ahead of the approaching
cold front. Rainfall amounts look to be generally in the 1-3"
range, with some potential for localized rain rates sufficiently
high enough to cause some urban/localized flooding concerns.

Hurley/Taylor


Day 3
Valid 12Z Fri Feb 14 2025 - 12Z Sat Feb 15 2025

...Southern California...
IVT plume weakens while pushing southward across SoCal to begin
the Day 3 Period. While the bulk of the event (Slight-Moderate
excessive rainfall risk) is expected on Day 2 or through Thursday
night, will maintain a Marginal Risk into the early part of Day 3
(Friday morning), especially if the southward AR progression slows down a bit.

...Mid South...
Amplifying longwave trough across the Southwest-4 Corners Region
Fri-Fri night will lead to backing mid/upper layer flow and
deepening WAA/moistening downstream within a maturing Warm Conveyor
Belt (WCB). Thermodynamic profiles will respond appreciably as a
result, especially late in the period (Fri night) as the low- level
flow backs SSW and increases (to 50+ kts at 850 mb). This leads to
robust low-level moisture transport late Friday night into early
Saturday morning, with 850-700 mb moisture flux anomalies ramping
up to 4-5 standard deviations above normal per the ensembles. There
will also be a corresponding uptick in elevated instability as
well, to the tune of 500-1000 J/Kg towards 12Z Sat. While the main
event will be on Saturday (see Day 4 ERO), will maintain the
Marginal Risk inherited from yesterday's Day 4 ERO given the
anticipation of the ingredients ramping up fairly quickly Friday
night, which given the probabilistic QPF along with the latest CSU UFVS-verified ERO first-guess fields, could lead to localized
runoff issues across portions of the Mid South. by the pre-dawn hours Saturday.

Hurley
$$
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FOUS30 KWBC 130812
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
312 AM EST Thu Feb 13 2025

Day 1
Valid 12Z Thu Feb 13 2025 - 12Z Fri Feb 14 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTHERN CALIFORNIA...

...California...
Overall, not much change to the previous forecast, with the
unfolding atmospheric river expected to peak near the start of the
period. A long warm front currently extending along the coast is
expected to press inland this morning, with IVTs climbing to around
700-800 kg/m/s near the upstream cold front as it approaches the
coast later this morning. The strongest moisture flux is expected
to center near SF Bay at the start of the period, before steadily
shifting south along the coast today. Models continue to show IVTs
decreasing as the axis moves south, dropping to around 400-500
kg/m/s as the AR reaches Southern California later this afternoon
into the evening. Guidance has remained fairly consistent,
indicating precipitation amounts of 4-6 inches along the central to
southern coastal ranges and the Sierra Nevada, falling mostly as
rain below 6000 ft.

A Moderate Risk (level 3/4) remains in place across portions
Southern California, from Santa Barbara County southeastward into
the San Gabriel and San Bernadino mountains, where damaging and
potentially life-threatening burn scar flash flooding and debris
flows remain a primary concern. Even outside of the burn scar areas,
intense rain rates over complex terrain and urban areas may produce
scattered to numerous instances of flash flooding. Elsewhere, a
broad Slight Risk (Level 2/4) exists for much of the remaining
coastal ranges as well as parts of the Central Valley and the lower
elevations of the Sierra Nevada.

...Florida Panhandle and Southern Georgia...

Lingering heavy rainfall will continue this morning across
portions of the Florida Panhandle and southern Georgia ahead of an
approaching cold front. HREF neighborhood probabilities indicate
that additional rainfall amounts of 1-2 inches are likely within
the highlighted area, with some potential for localized rain rates
high enough to cause some urban/localized flooding concerns.

Pereira


Day 2
Valid 12Z Fri Feb 14 2025 - 12Z Sat Feb 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID-SOUTH...

...Mid-South...

Although most of the convective activity, and thus heavy rainfall
threat, in the region should be concentrated in the Day 3 period
(after 12Z Saturday), model guidance does indicate that convection
is likely to begin blossoming late Friday Night. Conditions will
become increasingly favorable after 06Z Saturday with a strong 55-65
knot low-level jet expanding east from the Plains, and significant
northward moisture transport leading to rapid moistening of the
boundary layer. MUCAPE values of around 500-1000 j/kg should support
organized convection with the potential for rainfall rates in excess
of 1 inch per hour at times. Although there is a lack of a
significant front or boundary to help organize a band of convection,
the strength of the LLJ may support backbuilding within a broad zone
of developing convective clusters. This may be enough for some brief
training and a ramp-up in flash flood potential prior to 12Z
Saturday. The 00Z runs of the NAM Nest and FV3 show more widespread
convection than other models; if this trend persists as additional
hi-res guidance becomes available, an expansion of the Marginal Risk
and/or the addition of a Slight Risk area may become warranted with time.

...Southern California...

The Marginal Risk was removed for southern California given a more
limited QPF signal on the latest guidance, and hi-res models in
excellent agreement on a lack of organized convection. The bulk of
the threat should be in the Day 1 period.

Lamers


Day 3
Valid 12Z Sat Feb 15 2025 - 12Z Sun Feb 16 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE TENNESSEE AND OHIO VALLEYS AND THE CENTRAL APPALACHIANS...

...Ohio and Tennessee Valleys...

Confidence remains high in significant rainfall-related impacts on
Saturday and Saturday Night with model guidance in excellent
agreement depicting a swath of 3-6 inches of rainfall in the 24-hour
period across the region. Although models vary slightly with the
placement, they almost unanimously depict a corridor of heavy rain
about 750mi long centered somewhere in TN/KY. This same region has
generally seen above average precipitation in recent weeks, with the
14-day precip in much of KY, N TN, WV, and W VA at least double the
normal values. The confluence of these factors should make the
region especially vulnerable to flooding from the predicted
rainfall. For additional context on the current hydrologic picture
across the region, refer to the National Hydrologic Discussion from
the National Water Center at water.noaa.gov.

Convection may be ongoing at the beginning of the forecast period
and should become increasingly focused along a developing warm front
to the east of a surface low that will be emerging out of the Plains
on Saturday. The front will be positioned on the nose of very strong
SW, or even WSW, inflow, which should favor backbuilding and
training and a corridor of very heavy rainfall. The environment will
be atypical of mid-February with PWATs reaching around 1.5 inches
and MUCAPE of 500-1000 j/kg. For example, the Nashville sounding
archive exists back to 1948 and they've only ever reached 1000 j/kg
MUCAPE once in February, and 1.5 inch PWATs a few times. The
environment will support rainfall rates in excess of 1 inch per
hour, and given the potential for training and backbuilding, these
rates may be sustained for several hours in some locations. These
would be the areas of greatest concern for flash flooding -- not
only in terms of likelihood but severity -- particularly if the
higher rain rates are sustained over urban areas or vulnerable
terrain for extended periods of time.

The inherited Moderate Risk was mostly maintained as-is with a
slight expansion to the southwest in the vicinity of Memphis, TN;
and a more significant expansion eastward into S WV and W VA. The WV-
VA border region just received some significant snowfall, and model
guidance indicates a fairly high probability of warm, moist air (dew
points in excess of 45 degrees) accompanying the rainfall into this
area, which may lead to a combination of runoff from rain and snow melt.

It's worth noting a couple additional things. First, the amount of
rain forecast from E KY into S WV and W VA in particular is quite
unusual for the heart of the winter season. Calendar day precip
records across that area for January and February are generally in
the 2-3 inch range, and NBM probabilities indicate it is likely (60+
percent chance) we will see these types of 24-hour rainfall totals
in those areas. Second, this relatively rare winter rain event would
be delivered to an area that has been quite wet recently, and in
some areas has snow on the ground. And third, the high-end scenarios
in much of the Moderate Risk area would be significant by historical
standards. The NBM 90th percentile from N TN into S/E KY and S WV is
on par with the top several wettest days (for any season!) in the
station records in the area. This corridor is where the greatest
concern for severe impacts exists, and it's possible an upgrade to
High Risk may be needed for portions of the area in subsequent updates.

Lamers
$$
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